1. Field of the Invention
The present invention relates to a communication apparatus and a method of calculating a round trip time.
2. Description of the Related Art
TCP serving as a connection-type protocol uses several kinds of timers to avoid an interruption of communication. Time-out times to be set in the timers are determined by transmitting a segment having an arbitrary sequence number to the other end, measuring a round trip time until the sequence number is acknowledged, and reflecting the immediately preceding state of a transmission channel and that of the other end. Japanese patent No. 3476985 has proposed to adjust a transfer size in accordance with a measured round trip time.
Conventionally, round trip time measurement processing makes a next measurement after a measurement is completed. The measurement interval is therefore conventionally long. As a result, congestion occurs, and it is impossible to follow a sudden change in state such as a change in load of the other end.
As represented by a 10-gigabit network in recent years, the use of wideband communication media and incorporating a TOE (TCP/IP Offload Engine) in network devices have improved communication performance. There is, therefore, a demand for improving the accuracy of round trip time measurement.
In application examples such as moving image stream distribution and video conference systems in which contents are transmitted in real time, there is a demand for enhancing QoS. The key to enhancement of QoS is to grasp a short-term variation in round trip time and improve the accuracy of time measurement.